1. Preheat the oven to 400°F. Spray a baking sheet with nonstick spray.
2. Heat 1 teaspoon of oil in a small nonstick skillet over medium heat. Add the onion, celery, and bell pepper; cook, stirring occasionally, until the vegetables soften, 4-5 minutes. Transfer to a bowl and let cool about 5 minutes. Add the crabmeat, parsley, mayonnaise, worcestershire, and 1/4 teaspoon of the salt; toss gently.
3. Place the flounder fillets on a work surface so that the skin side is facing down. Brush with the remaining 2 teaspoons oil and sprinkle with the remaining 3/4 teaspoon salt. Turn the fillets over and top each with a quarter of the crab mixture placed 1 1/2 inches from the tail end of each fillet. Fold the tail ends over the crab and roll up. Place the rolled fillets on the baking sheet, seam side down; sprinkle with the paprika.
4. Bake until the flounder is opaque in the center and the filling is hot, about 18-20 minutes.